The present invention relates to retrieving data from a mass storage device, specifically to the operation of a pointing device which directs traffic in transferring blocks of data from the mass storage device to a buffer memory region.
The advent of large mass storage media associated with personal computers has resulted in demand for more efficient means to access data for processing. The main objective of the present invention is to provide an efficient and cost effective way of channeling blocks of data from a large but slow storage medium (i.e., tape drives, compact disk read-only-memory, etc.) into a faster main memory region for immediate processing by the central processing unit.
In general, input and output (I/O) operations to mass storage devices are controlled through the operating system of the computer. A user task which needs data from one of these devices requests the data by invoking a system function which is defined in the operating system. This function may, for example, invoke the memory management function of the operating system to allocate a buffer to receive the requested data; translate the user's request into an I/O command; and send the command to the controller for the requested device. When the device controller has transferred the requested data, another operating system routine may be invoked to ensure that the operation completed without error and to notify the user task that the requested data is available.
In some computer systems, disk caching or buffering schemes are used to speed-up access to a large mass of data from a slow storage unit. For example, the patent to Barret et al. (U.S. Pat. No. 5,136,692) concerns a storage driver which includes multiple memory buffers designed to hold data retrieved from a disk storage device. The storage driver sequentially reads data blocks from the disc and stores the blocks in the buffers. Here, the storage driver additionally accesses non-requested data in anticipation of future requests by the system. The buffers containing data are marked as available for processing as soon as the processor command which reserved the blocks is no longer active. Non-requested data typically remain in buffers until requested by the processor. However, in the event no request for this extra data is made by the processor and a buffer is needed for a new I/O request, this non-requested extra data is overwritten to make room for the new data.
These existing methods of handling I/O operations to mass storage devices require excessive system software involvement by requiring each I/O operation to be both initialized and terminated, forcing undesirable transfer delays. The operation is further delayed by the need to allocate and reserve the I/O buffers.